A formula used by firearms and toolmark examiners to clean lead residue from bullets was also found to remove excess gun blue coating from metal cartridge cases. It consists of a mixture of acetic acid and hydrogen peroxide and works by oxidizing the coating back into solution. This explanation allows one to determine the optimum proportion of the mixture. Acidified hydrogen peroxide formulas were also found to “clean” (oxidize or etch) metal cartridge cases in areas where there was no sebaceous latent print material (or other substances that resist oxidation). The subsequent treatment of these “cleaned” cartridge cases with gun blue to enhance the latent print contrast was also considered.

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